The Frequency and Demographics of Massive Black Hole Pairs and Binaries: from Tens-of-kpc to Sub-pc Scales

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Question: Is there an observational constraint on the abundance of massive black hole

The Frequency and Demographics of Massive Black Hole Pairs and Binaries: from Tens-of-kpc to Sub-pc

Civano, Paul Green (CfA) IFU spectroscopy: Aaron Barth (UCI), Julia Comerford (Austin) VLBA/eVLA

1 Question: Is there an observational constraint on the abundance of massive black hole pairs/binaries in galactic nuclei? The Frequency and Demographics of Massive Black Hole Pairs and Binaries: from Tens-of-kpc to Sub-pc Scales Yue Shen (CfA), Michael Strauss, Jenny Greene (Princeton) Lei Hao (SHAO); X-ray: Francesca Civano, Paul Green (CfA) IFU spectroscopy: Aaron Barth (UCI), Julia Comerford (Austin) VLBA/eVLA imaging: Joseph Lazio (JPL), Joan Wrobel (NRAO) Spectroscopic monitoring: Fuyan Bian (UA), Mike Eracleous (PSU), Avi Loeb (CfA), Scott Tremaine (IAS) Xin Liu

Massive black hole pairs/binaries are expected in galactic nuclei mergers are generic to the hierarchical galaxy buildup most local galaxies host a

of Hawaii)/John Hibbard (NRAO); Animation: NASA/CXC/A.

2 Massive black hole pairs/binaries are expected in galactic nuclei mergers are generic to the hierarchical galaxy buildup most local galaxies host a massive black hole at center massive BH pairs/binaries: galaxy evolution s natural product Simulation: Josh Barnes (U. of Hawaii)/John Hibbard (NRAO); Animation: NASA/CXC/A. Hobart probe both fundamental physics and galaxy evolution Spri ngel & Hernquist 2003 MBBH abundance calibrates the expected rate of gravitational wave sources. MBBHs may be crucial for understanding a variety of astrophysical phenomena (e.g., see reviews by Komossa 06, Colpi & Dotti 09).

3 Problem: direct evidence scarce Question: how common? are they intrinsically special? known AGN pairs/binaries pre C 75 Chandra X-ray + VLA Radio DSS Optical + VLA Radio NGC 6240 Komossa+03, Ballo+04, Hudson+06, Maness+04, Rodriguez+06, Bianchi+08

as of 2011 SDSS J1027+1749 3kpc Comerford+10, Green+10,

4 Significant progress made recently systematic searches statistical analysis feasible known AGN pairs/binaries as of 2011 SDSS J kpc Comerford+10, Green+10, Liu+10, Fu+11, Greene+11, Koss+11, Liu+11a, McGurk+11, Shen+11

5 dynamical range and gas physics involved pose a challenge for theory Begelman, Blandford & Rees 80; see a recent review by Colpi & Dotti 09 pairing binary GW hardening cartoon by C. Zier

6 How to identify massive black hole pairs/binaries? dormant binaries stellar cores in elliptical galaxies (e.g., Kormendy+09) hypervelocity stars (Yu & Tremaine 2003; Lu, Yu & Lin 2007) tidal disruption flare (e.g., Ivanov et al. 2005; Chen et al. 2008, 2009) gravitational lensing (Li, Mao, et al. 2012) active pairs/binaries In an ideal world, a super sensitive, high-resolution hard X-ray all-sky survey! in the real world, an optical spectroscopic survey based on the identification of AGNs (as signpost for active massive black holes) statistical databases (of galaxy mergers and AGNs) needed complementary approaches needed for different regimes 6

7 I. early pairing phase: onset of a cosmic collision pairing binary GW hardening cartoon by C. Zier

8 Identification Step1: select by imaging Step2: identify by spectra, and correct for spectroscopic incompleteness 14 kpc SDSS optical Observed wavelength (A)

9 Liu, Shen, Strauss, Hao (2011a) 9

10 A statistical sample of AGN pairs is available. AGN pairs from the SDSS DR7: the frequency on kpc scales (Liu, Shen, Strauss, & Hao 2011a) sample selection 138,070 optically identified AGNs at z<0.33 from SDSS DR7 select pairs with r p <100 h 70-1 kpc, dv < 600 km/s and a tidal subset correct for spectroscopic incompleteness ~30% of the sky in SDSS overlapping Plates (free from fiber collision) 10

11 Frequency how many single/double AGNs among all galaxy pairs? Liu+11b 1. for L bol > erg/s, f AGN increases for closer pairs! 2. double AGNs correlate at < 20 kpc.

12 evidence for tidally enhanced recent host star formation young galaxy old galaxy SSFR increases by 0.9+/-0.2 dex from 100 to 5 kpc Kauffmann+03 Liu, Shen, Strauss (2011b)

13 evidence for tidally enhanced black hole accretion Eddington ratio increases by 0.5+/-0.1 dex from 100 to 5 kpc Shen+11 see also Heckman+05, Reyes+08 Liu, Shen, Strauss (2011b)

14 Summary for part I. the early-pairing phase AGN pairs are out there not elusive! Their frequency indicates tidally enhanced accretion in galaxy pairs on top of a background of stochastic accretion (not associated with mergers). There is evidence for tidally enhanced host recent star formation and black hole accretion, which becomes more significant at smaller separations, as well as correlation between the two BHs. Ongoing/future work: X-ray properties, detailed characterization of host galaxies (IFU spectroscopy) a 3D map of gas, stars, and radiation 14

15 II. late-pairing phase: setting the stage for binaries pairing binary GW hardening cartoon by C. Zier

16 Why kpc scales? tidal perturbations become significant (making nuclear activity more likely, enabling identification via AGN diagnostics) disks are being turned into bulges effects on host galaxies precursors of binaries set the stage for subsequent evolution kpc-scale pairs can still be spatially resolved and therefore be unambiguously confirmed using current facilities ground-based OIR HST Chandra X-ray VLBA ~0.5 w/o AO ~0.1 w/ AO ~0.1 ~0.5 ~ mas selection based on resolved mergers in SDSS images is biased against the late-pairing phase a different approach is needed 16

17 Identification Step 1. select by kinematic features (spatially integrated) Step 2. identify by high-resolution imaging + spatially resolved spectroscopy spatial SDSS optical 1.5 kpc Step 3. confirm by X-ray/radio imaging spectroscopy and/or IFU spectroscopy HST WFC3/IR Magellan/LDSS3 wavelength SDSS Optical VIRUS-P IFU

18 normal AGNs show single-peaked narrow lines random motion of ionized gas clouds flux density Hβ4863 Urry & Padovani (1995) Wavelength 5/Glossary/Essay_seyfert.html Data courtesy of A. V. Filippenko 18

Emission-line velocity splitting has long been known (e.g., Sargent 1972; Heckman et al. 1981; Whittle 1985; Veilleux 1991) [O III]4959,5007 Hβ4863 Heckman et al.

19 Emission-line velocity splitting has long been known (e.g., Sargent 1972; Heckman et al. 1981; Whittle 1985; Veilleux 1991) [O III]4959,5007 Hβ4863 Heckman et al. (1981) Wavelength flux density scenario1: NLR gas kinematics (e.g., Axon et al. 1998; Veilleux et al. 2001; Crenshaw et al. 2009; Fisher) M. Whittle (arcsec) 19

20 scenario 2: merging MBH pairs? (e.g., Heckman et al. 81; Zhou et al. 2004; Gerke et al. 2007; Comerford et al. 2009) blueshifted redshifted cartoon from Christian Zier systemic 20

21 AGNs with double-peaked narrow lines: gas kinematics or merging MBH pairs? (Can we distinguish between them? Yes.) Step 1. select candidate agn pairs via their kinematics signature a sample of 167 doublepeaked narrow-line AGNs at z~0.15 from SDSS DR7 -- 1% of parent AGNs (Liu+10a; see also Wang+09 and Smith+10 for similar statistical studies) statistical properties are inconclusive SDSS data alone not good enough: image resolution limited fiber spectra lack spatial information need follow-up observations to determine the nature Liu, Shen, Strauss, Greene10a 21

22 Step 2-a: higher resolution NIR imaging to identify double stellar bulges (each associate w/ its own MBH); NIR advantage: less affected by dust Magellan/PANIC ~0.4 FWHM in K s Liu, Greene, Shen, Strauss (2010b) 22

23 Step 2-b: spatially resolved spectroscopy to locate ionizing sources Magellan/LDSS3 slit spectroscopy, 0.8 in r Liu, Greene, Shen, Strauss (2010b) SDSS spectrum Magellan/LDSS3 spectrum 23

24 the double-peak approach is feasible for identifying kpc-scale binary AGNs four kpc-scale binary AGNs identified from 43 DP AGNs Liu, Greene, Shen, Strauss, Greene10b 24

25 an important (and often overlooked!) caveat of the double-peak approach many objects show spatially offset [O III] emission with a smooth stellar background on similar scales Shen, Liu, Greene, Strauss (2011) ~10% dual AGN, ~50% single AGN kinematics, ~40% ambiguous emphasize the importance of combining imaging and slit spectroscopy in identifying kpc-scale binary AGNs spatial Hβ [O III] 4959, 5007 wavelength Magellan/PANIC Ks favor gas kinematics scenarios for the majority of DP AGNs (Shen et al. 2011). APO 3.5m/DIS slit spectrum Shen et al. in prep 25

26 Summary for part II. the late-pairing phase The double-peak narrow-line approach is feasible for identifying kpc-scale binary AGNs. The observed frequency is consistent with expectation from the merger hypothesis (Yu, Lu et al. 2011) It is premature to claim binary AGN based on either imaging or spatially resolved [O III] emission alone (Shen et al. 2011). future work: X-ray confirmation; detailed properties with IFU 3D mapping; explore a more advanced merger phase (ongoing HST program) 26

27 III. the binary phase pairing binary GW hardening cartoon by C. Zier

28 Question: What is the observational constraint on the abundance of massive black hole binaries in galactic nuclei? Spectroscopic Monitoring of Quasars with Shifted Broad Emission Lines: Testing Candidate Binary Massive Black Holes Xin Liu (CfA), in collaboration with: Yue Shen (CfA), Michael Strauss (Princeton), Fuyan Bian (Arizona), Abraham Loeb (CfA), Scott Tremaine (IAS) based on data from MMT, ARC 3.5m, FLWO 1.5m, and SDSS DR8

29 Massive black hole binaries should be common BBR80 Begelman, Blandford & Rees 80 Milosavljevic & Merritt 01, Yu 02 most likely observations - come from longest phases orbital decay may slow down at ~ pc scales (e.g., due to loss cone depletion) gas/stellar processes help dump angular momentum, but entering the GW phase still takes > 10 8 yr

Problem: direct evidence for MBBHs is elusive CSO 0402+379 (Maness+04, Rodriguez+06): two compact, flat-spectrum VLBI radio sources

30 Problem: direct evidence for MBBHs is elusive CSO (Maness+04, Rodriguez+06): two compact, flat-spectrum VLBI radio sources (r p = 7 pc) another candidate (debatable): OJ 287 (Valtonen+08) Rodriguez+06 VLBI imaging measuring abundance needs systematic surveys

31 How to identify BBHs? direct imaging is (relatively) clean, but even VLBI cannot resolve most of the purported stalled binaries Burke-Spolaor (2011), ~ mas resolution no evidence for additional binaries in 3114 radio-luminous AGN from VLBI archive best chance likely in local galaxies (ref. J. Condon), but limited by AGN space density and radio activity requirement

32 How to identify BBHs? dynamical signal: double-peaked BELs? probably not. J BBH (Boroson & Lauer 09)? or an unusual disk emitter (e.g., Chornock+ 10; Gaskell 10)? Binary? Gaskell (1983), but long-term variability favors disk emitter (e.g., Chen+89, Eracleous & Halpern 94) normal AGN Vanden Berk+ 01 BBHs are not expected to show wellseparated double peaks (e.g., Yu 02, Shen & Loeb 10). DP-BEL AGN Harpen+96

33 How to identify BBHs? dynamical signal: shifted single-peaked BELs? maybe. shifted BEL AGN 3C 227, Mrk 668 (Gaskell 83, 84) SDSS J (Decarli + 10) SDSS J (Bogdanovic+09, Dotti+ 09; but see Komossa+ 08, Shields+09, Heckman+09 for alternative scenarios). SDSS J (Shields+ 09) analogous to single-lined spectroscopic binary star Working hypothesis: only one BH is active Gaskell 83 systematic samples available: Shen+ 10, Tsalamantza+11, Eracleous+11 (see also Bonning+07) problem: dynamical arguments based on single-epoch spectra are ambiguous.

34 Temporal velocity drift offers a powerful diagnostic instrumental in rejecting the binary hypothesis for several DP BELs. most periods longer than ~a decade, therefore need dedicated long-term program For sub-pc binaries with periods of centuries, velocity drifts should be ~200 km/s per decade. Eracleous+ 97 orbital decay by GWs starts at (Loeb 10): The pioneering study by Eracleous et al. (2011) focused on extreme offsets (v off > 1000 km/s). Larger drifts are expected at smaller v off (e.g., Bogdanovic+ 09)

35 Preliminary results suggest 20% show significant velocity drifts Start from Shen+ 10 sample, based on SDSS DR8 focus on well-defined, single-peaked, shifted BELs focus on small yet significant v off control sample from SDSS: ~ 500 normal quasars with repeated spectra started in 09, as of Jan 12, got second-epoch spectra for ~50 out of ~300 obj. ~10 yrs after SDSS spectra examples: drift in peak position change in line width

36 Summary for part III. the binary phase MBH binaries should be common, but direct evidence is elusive. Direct imaging is limited, so must rely on dynamical signature. Unlike extreme DP BELs, AGNs with shifted broad lines are promising candidates, but single-epoch spectra are not enough. Dedicated, long-term spectroscopic monitoring (together with other complementary tests, e.g., observing UV lines, reverberation mapping, high-resolution imaging to test the alternative recoil hypothesis) is needed. It is hopeful to expect strong candidates. Stay tuned!

37 Conclusion AGN pairs: enhanced accretion at small separations, sitting on top of a background stochastic accretion in galaxy mergers double-peaked approach is feasible to identify kpc-scale binary AGNs, despite significant contamination from gas kinematics spectroscopic monitoring of shifted-broad-line AGNs is a promising tool to constrain stalled binaries future work - smaller separations -higher luminosities - effect of early-stage activity on the host galaxy -coupled dynamical evolution and accretion Chandra HST, ground-ao GSMT VLBA spectroscopic monitoring LSST

Dual Supermassive Black Holes as Tracers of Galaxy Mergers. Julie Comerford

Dual Supermassive Black Holes as Tracers of Galaxy Mergers Julie Comerford NSF Astronomy and Astrophysics Postdoctoral Fellow University of Texas at Austin Collaborators: Michael Cooper, Marc Davis, Mike